Field of the Invention
The present invention relates to a broadband wireless communication system, and in particular, to an apparatus and a method for controlling a terminal accessing a base station in a broadband wireless communication system.
Description of the Related Art
In a 4th generation (4G) communication system, research for providing services having various Quality of Service (QoS) using transmission speeds of about 100 Mbps is in active progress. Particularly, research for supporting high speed services in the form of guaranteeing mobility and QoS for a broadband wireless access (WBA) communication system, such as short-distance wireless communication network system and wireless metropolitan area network (WMAN) system, is in active progress. As an example, communication systems complying with the Institute of Electrical and Electronics Engineers (IEEE) 802.16 specification is representative of such a system.
The IEEE 802.16 system standard defines various procedures, such as the operation of a Media Access Control (MAC) layer. Examples of MAC layer procedures include an initial ranging procedure and a handover procedure. Described below are procedures for initial ranging and handover initiated by a terminal in accordance with the IEEE 802.16 system standard.
The initial ranging procedure according to the IEEE 802.16 system standard is performed as follows. To initiate initial ranging, a terminal transmits one of a plurality of prescribed ranging codes to a base station. In response thereto, the base station transmits a response message RaNGing ReSPonse (RNG_RSP) message to the terminal. The RNG_RSP message includes ranging status TypeLengthValue (TLV). If the base station is in a status that does not allow ranging of the terminal (i.e., the entry of the terminal to the base station), the base station sets the ranging status TLV to “abort” to inform the terminal of a ranging-not-allowed status. Accordingly, the terminal detects when its request for entry is not allowed and then scans other base stations for entry.
The handover procedure according to the IEEE 802.16 system standard is performed as follows. To initiate handover, a terminal scans neighboring base stations and transmits information of scanned neighboring base stations MOBile_Mobile Station HandOver-REQuest (MOB_MSHO-REQ) message that includes information of target base station candidates to its serving base station. Accordingly, the serving base station confirms whether the target base station candidates included in the MOB_MSHO-REQ message received from the terminal can support service for the terminal. At this point, the serving base station transmits a MOBile_Base Station HandOver-ReSPonse (MOB_BSHO-RSP) message indicating that a target base station has been found to the terminal. The MOB_BSHO-RSP message includes information of the target base station candidates that can provide the requested handover. The terminal that has received the MOB_BSHO-RSP message selects a target base station and transmits a MOBile_HandOver-INDication (MOB_HO-IND) message to inform the serving base station of the selected target base station. The serving base station that has confirmed the target base station selected by the terminal provides information regarding the terminal to the target base station, and the terminal performs an entry procedure to connect to the target base station.
As described above, the base station can limit entry of the terminal during the initial ranging procedure. However, the base station cannot prevent the terminal from immediately trying to access the base station again, that is, retrying the initial ranging procedure. When the terminal immediately re-requests the base station for entry, there is a high possibility that the entry request will be denied again since the status of the base station has not yet changed. Therefore, immediately requesting entry again by the terminal causes waste of wireless resources. In addition, a terminal that has performed handover to change the serving base station may initiate handover again to the previous serving base station. Repeatedly performing handover between two base stations also causes waste of wireless resources, and repeatedly attempting handover itself wastes wireless resources. Therefore, there is a need to prevent unnecessary attempts for entry as well as actual execution of entry procedures.